Rechargeable power supply system and method of protection against abnormal charging

ABSTRACT

An intelligent battery comprising a battery cell for charging and discharging; a voltage detection circuit for detecting voltage of the battery cell; a current detection circuit for detecting charging current; a charging-stop FET for stopping charging for the battery cell; and a CPU for activating the charging-stop FET based on voltage detected by the voltage detection circuit, wherein before the voltage reaches a voltage for activation of the charging-stop FET, when the charging current value detected for the battery capacity by the current detection circuit is larger than a reference, the CPU determines that an abnormal state occurs, and activates the charging-stop FET. The present invention provides, in part, a battery, which is safer even if dual accidental malfunctions occur.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a power supply system having a batterythat can be used by repeated charging/discharging (secondary battery),more particularly, to a power supply system having a protection facilityagainst abnormal charging.

2. Background of Related Art

In various devices and apparatuses (such as notebook-sized personalcomputers (notebook PCs), PDAs, information terminal equipment includingmobile phones, Mini Disc (MD) drives, and video cameras), secondarybatteries are extensively employed as a battery that can be used manytimes by repeated charging/discharging. As a secondary battery, oftennickel-hydrogen batteries or nickel-cadmium batteries are used, wheresuch use is employed typically since these types of batteries areinexpensive and have larger capacity. Additionally, other typesincluding lithium ion batteries, having higher energy density per unitweight than the nickel-cadmium batteries, and lithium-polymer batteries,that uses a solid polymer instead of a liquid electrolyte, may also beused.

If a secondary battery such as a nickel-hydrogen battery, anickel-cadmium battery, a lithium ion battery, or a lithium-polymerbattery, is in an over-charging state or an over-discharging state,problems such as lowered performance, damaged electrodes, orshort-circuits inside the battery may occur.

For example, in Published Unexamined Patent Application No. 6-86469(Japan Patent Office) the specification discloses a technique for thealarming of short-circuits by generating signals based on the detectionof a lowered battery voltage and short-circuits within the battery.Additionally, in Published Unexamined Patent Application No. 2000-102185Japan Patent Office), the specification discloses a technique whereineach secondary battery cell in a first battery group and each secondarybattery cell in a second battery group are connected separately formonitoring/controlling purposes, such that if an internal short-circuitoccurs in one of the battery groups, a short-circuit current isprevented from flowing into the secondary battery cells in the otherbattery group.

However, in above-referenced Published Unexamined Patent ApplicationNos. 6-86469 and 2000-102185 described above and incorporated byreference herein, when an internal short circuit occurs in a conditionwhere the battery is charged to a voltage above a predetermined voltagedue to a malfunction of the apparatus, it is impossible to prevent abattery from being in a dangerous state while short-circuit current canbe prevented from flowing into batteries. As a result, it is generallyknown that when an internal short-circuit in a battery cell occurs inaddition to overvoltage in the battery, the condition of the batterybecomes dangerous.

In order to charge a secondary battery (battery-pack) a charger is oftenused with an alternating current (AC) adapter. When a short-circuitbreakdown occurs in either a switching transistor in the charger or ashort-circuit prevention transistor for preventing short-circuit in thecharger, the AC adapter and the battery short-circuit electrically,resulting in an abnormal charging of the battery (first error). In thiscase, charging continues until a primary protection circuit in thebattery pack goes into operation. At this point, the battery voltage,for example in the case of lithium-ion battery, is about 4.35 V/cell. Ifadditionally a short-circuit occurs in the battery cell, a dangerousstate (second error) is possible. These dangerous states as well as asituation where the battery is in a high temperature environment shouldbe taken into consideration in designing.

Currently, intelligent batteries having a CPU built-in in a battery pack(secondary battery) are widely used. For example, a lithium ion batteryconstituting an intelligent battery is used, in which a charging stopFET (charging protection circuit) and a discharging stop FET(discharging protection circuit) are built in a battery pack. The CPU inthe battery pack monitors the voltage in the battery by inputting asignal from a voltage detection circuit, then analog-to-digital (A/D)converting the signal inside it. In this battery pack, when the voltagereached 4.35 V or higher, for example, it is determined that abnormalcharging occurs, and the charging is aborted by turning off the chargingstop FET. Since the battery voltage in full charging (100% charging)state is 4.2 V (±50 mV), the current design in which abnormal chargingis detected at 4.35 V/cell is considered to be proper taking detectionerror and other factors into consideration.

However, while a safety state can be maintained in a normal condition, adangerous state becomes possible, when in a condition charged to 4.35 Vfurther occurs a malfunction such as internal short-circuit in thebattery cell. It is therefore necessary to accommodate the worst casetaking conditions such as ambient temperature into consideration.

SUMMARY OF THE INVENTION

The present invention is made to solve and overcome the technicalproblems described above, as well as other known limitations in the art.It is an object of the present invention to provide a battery, which issafer, even where double accidental malfunctions occur.

An object of the present invention is to operates to maintain safety,such that when a short-circuit occurs in a battery cell, and when thebattery is charged to a voltage above a predetermined voltage due to amalfunction of a connected charger (or a portion of an apparatus), toabove charging by detecting a malfunction of the charger (or the portionof the device) before the conventional first overvoltage protectionfacility is activated.

Therefore, in one aspect, the present invention is a power supply systemwith a battery for supplying power to a main system, comprising:charging current measuring means for measuring charging current for thebattery; battery capacity calculation means for calculating(integrating) battery capacity of the battery; detection means fordetecting malfunction occurring in the battery based on a chargingcurrent value obtained and the battery capacity calculated (malfunctionoccurrence detection means); protection facility activating means foractivating a protection facility based on detection of malfunctionoccurrence; and notification means for notifying the main system ofmalfunction occurrence based on detection of the malfunction.

The detection means (malfunction occurrence detection means) ispreferably adapted, for example, to detect malfunction occurrence basedon information in a table for malfunction detection, showing therelation between battery capacity and malfunction detection currentvalue. The detection means can also be adapted to detect malfunctionoccurrence based on an equation representing the relation betweenbattery capacity and charging current value, which equation isseparately defined according to battery capacity.

In another aspect, the present invention is also a computer device,comprising: a main system for data processing; and an intelligentbattery for supplying power to the main system, wherein the intelligentbattery comprises: a battery cell for charging and discharging; acurrent detection circuit for detecting charging current for the batterycell; a CPU for calculating battery capacity by integrating detectedcharging current, and recognizing malfunction occurrence occurring inthe battery based on charging current value detected by the currentdetection circuit and the battery capacity calculated; and a protectioncircuit for performing stop operation according to instruction from theCPU based on recognition of malfunction by the CPU.

In a further aspect, the present invention may also be understood to bea battery connected to a main system of a computer device or the like(intelligent battery). Thus, a battery according to the presentinvention, comprises: a battery cell; a voltage detection circuit fordetecting voltage for the battery cell; a current detection circuit fordetecting charging current for the battery cell; a charging stop unitfor stopping charging for the battery cell; and a control unit foractivating the charging stop unit based on voltage detected by thevoltage detection circuit, wherein before the voltage reaches a voltagefor activating the charging stop unit, the control unit detects anabnormal state based on a charging current value detected by the currentdetection circuit, and activates the charging stop unit.

In another aspect, the present invention is a method for protecting abattery from abnormal charging, comprising: measuring a charging currentvalue for the battery; calculating integrated capacity for the battery;and activating a protection facility when the charging current valuemeasured for the calculated integrated capacity is larger than apredetermined value. The method is preferably characterized in that theprotection facility is activated based on information such as tableinformation or an equation, specifying a reference value representing acharging current value at which a malfunction is detected for anintegration capacity, since malfunction occurring can be detected assoon as abnormal current for an integrated capacity flows. Theprotection method can also provide a battery with excellent safety sincethe protection facility can be activated in the state where theintegrated capacity is less than 100%.

In another aspect, a method for protecting from abnormal chargingaccording to the present invention is characterized for example, in thatit comprises: recognizing that a battery is connected to an apparatussuch as a typical notebook PC with a charger forconstant-current/constant-voltage charging, by using ID or the like thatis identification information delivered from the apparatus; measuringcharging current value when the battery is charged while switching fromconstant-current charging to constant-voltage charging, determiningbased on the measured charging current value whether abnormal chargingoccurs or not; and aborting charging when it is determined that abnormalcharging occurs.

In yet another aspect, the present invention may also be understood asprograms for enabling in a microcomputer contained a battery to performeach of these functions. The programs can be provided to a microcomputera processing unit from a remote program transmission device via anetwork, for example. The program transmission device may be configuredto comprise storage means such as a CD-ROM, a DVD, a memory or ahard-disc with the programs stored therein, and a transmission means forreading the programs from the storage means and transmitting theprograms to a device for executing the programs, via connectors andnetworks such as Internet or LAN. The programs may be provided by usinga storage medium such as CD-ROM.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects, features, and advantages of the present invention willbecome more fully apparent from the following detailed description, theappended claims, and the accompanying drawings in which:

FIG. 1 shows a hardware configuration of a computer system to which anembodiment of the present invention is applied;

FIG. 2 shows a configuration of an intelligent battery comprising anabnormal charging protection function according to an embodiment of thepresent invention;

FIGS. 3(a) and (b) show charging characteristics of a lithium ionbattery;

FIG. 4 shows a relationship between battery capacity and chargingcurrent in a normal charging;

FIGS. 5(a) and (b) show an example of determination criteria formalfunction detection used in an embodiment of the present invention;

FIG. 6 is a block diagram of processes performed in CPU of theintelligent battery;

FIG. 7 is a flow chart showing process flow in the case where the tableshown in FIG. 5(a) is used; and,

FIG. 8 is a flow chart showing a flow of abnormal state detectionprocess based on numeral formulas.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a diagram showing a hardware configuration of a computersystem 10, for an embodiment of the present invention.

A computer device comprising this computer system 10 is configured as anotebook-size of personal computer (notebook PC) having a predeterminedoperation system (OS) loaded therein, preferably in compliance with OpenArchitecture Developer's Group (OADG) specification, for example.

In the computer system 10 of FIG. 1, a CPU 11 functions as theoperational brain of the entire computer system 10, and executes variousprograms under the control of the OS. The CPU 11 is interconnected withvarious units via three buses: Front Side Bus (FSB) 12 as a system bus;Peripheral Unit interconnect (PCI) bus 20 as a bus for high speed I/Odevice; and Industry Standard Architecture (ISA) bus 40 as a bus for lowspeed I/O device. This CPU 11 is designed to increase processing speedby storing program codes or data in cache memories. Typically, a SRAM ofabout 128K bytes is integrated in the CPU 11 as a primary cache,although more and less are foreseen by the present invention. However,in order to make up for capacity shortage, a secondary cache 14 of about512K to 2M bytes is connected to the CPU via a Back Side Bus (BSB) 13that is an exclusive bus. It is also possible to eliminate the BSB 13and to connect the secondary cache 14 to FSB 12 so as to avoid use of apackage with many terminals, thereby reducing the cost.

The FSB 12 and the PCI bus 20 are in communication with a CPU bridge 15called memory/PCI chip (host-PCI bridge). The CPU bridge 15 comprises amemory control function for controlling operation to access a mainmemory 16, a data buffer for buffering difference in data transfer ratebetween the FSB 12 and the PCI bus 20, and so on. The main memory 16 isa writable memory used as an area for reading an execution program forCPU 11, or a working area to which process data for the executionprogram is written. For example, it consists of several DRAM chips,equipped with a 64 MB chip for example, as its standard, havingcapability of expansion up to 320 MB. The execution program includes OSand various drivers for hardware operation of peripheral devices,application programs intended for specific work, and firmware such asBasic Input/Output System (BIOS) stored in a flash ROM 44 that will bedescribed later.

A video subsystem 17 is a subsystem for implementing a function forvideo, and includes a video controller. The video controller processes arendering instruction from the CPU 11 to write the processed renderinginformation to a video memory, and to read out the rendering informationfrom the video memory so as to output it as rendering data on a liquidcrystal display (LCD) 18.

The PCI bus 20 is a bus that allows relatively high-rate data transfer,and standardized by a specification with data bus width of 32 bits, 64bits, maximum operation frequency of 33 MHz, 66 MHz, and maximum datatransfer rate of 132 MB/sec, 528 MB/sec. An I/O bridge 21, a card-buscontroller 22, an audio subsystem 25, a docking station interface (DocI/F) 26, and a mini PCI connector 27 are connected to the PCI bus 20,respectively.

The card-bus controller 22 is an exclusive controller for directlycoupling a bus signal on the PCI bus 20 with an interface connector(card bus) of a card-bus slot 23. A PC card 24 can be inserted to thecard-bus slot 23. The docking station interface 26 is hardware forconnecting a docking station (not shown) that is a function expansiondevice of the computer system 10. When a notebook PC is set in thisdocking station, the various hardware units connected to the internalbuses of the docking station are connected to the PCI bus 20 via thedocking station interface 26. A mini PCI card 28 is connected to themini PCI connector 27.

The I/O bridge 21 comprises a bridge function between the PCI bus 20 andthe ISA bus 40. It also comprises a DMA controller function, aprogrammable interruption controller (PCI) function, a programmableinterval timer (PIT) function, Integrated Device Electronics (IDE)interface function, a Universal Serial Bus (USB) function, and a SystemManagement Bus (SMB) interface function. The I/O bridge also preferablyhas a built-in real time clock (RTC).

The DMA controller function is a function for performing data transferbetween peripheral devices such as FDD and the main memory 16 withoutpassing through the CPU 11. The PCI function is a function forresponding to interruption request (IRQ) from a peripheral device toexecute a predetermined program (interruption handler). The PIT functionis a function to generate timer signal with a predetermined frequency.An IDE hard-disc drive (HDD) 31 is connected to the interfaceimplemented by the IDE interface, and a CD-ROM drive 32 is ATAPI (ATAttachment Packet Interface) connected to the interface. Instead of theCD-ROM drive 32, another type of IDE device such as Digital VersatileDisc (DVD) drive may be connected to the interface. External storagedevices such as the HDD 31 or the CD-ROM drive 32, are accommodated, forexample, in an accommodation place in a notebook PC body, called “mediabay” or “device bay”. Theses external storage devices equipped as astandard may be installed in an exchangeable and exclusive manner withother devices such as FDD and a battery pack.

The I/O bridge 21 is provided with a USB port, which is connected to aUSB connector 30 disposed, for example, on a wall surface of a notebookPC body. An EEPROM 33 is connected to the I/O bridge 21 via SM bus. TheEEPROM 33 is a memory for storing information such as a password orsupervisor password registered by the user and the product serialnumber, and is non-volatile, and electrically rewritable for storedcontent.

The I/O bridge 21 is also connected to a power supply circuit 50. Thepower supply circuit 50 comprises an AC adapter 51 connected to acommercial main of AC 100 V, for example, for AC/DC conversion, anintelligent battery 52 as a battery (secondary battery), a batteryswitching circuit 54 for charging the intelligent battery 52 andswitching power feeding paths from the AC adapter 51 and the intelligentbattery 52, and a DC/DC converter (DC/DC) 55 for generating constant DCvoltages used in the computer system 10, such as +15 V, +5 V, and +3.3V. The intelligent battery 52 may removable from the main system as abattery pack, and may also be provided inside the housing of the mainsystem.

In a core chip composing the I/O bridge 21, an internal register formanaging a state of the power supply 10, and a logic for managing astate of the computer system 10 including the operation of the internalregister (state machine) is provided. This logic transmits to/receivesfrom the power supply circuit 50, various signals. The logic recognizesthe actual state of feeding from the power supply circuit 50 to computersystem 10 by the transmission/reception of the signals. The power supply50 controls the power feeding to the computer system 10 according toinstructions from the logic.

The ISA bus 40 is a bus with a data transfer rate lower than the PCI bus20 (for example, bus width: 16 bits, maximum data transfer rate 4MB/sec). An embedded controller 41 connected to a gate array logic 42, aCMOS 43, a flash ROM 44, and a Super I/O controller 45 are connected tothe ISA bus 40. The ISA bus 40 is also used for connecting peripheraldevices operating in relatively low speed such as keyboard/mousecontroller. An I/O port 46 is connected to the Super I/O controller 45,and controls driving of FDD, input/output of parallel data via aparallel port (PIO), and input/output of serial data via a serial port(SIO).

The embedded controller 41 controls keyboard (not shown), and isconnected to the power supply circuit 50 to support in part the powersupply management function by means of a built-in power managementcontroller (PMC) in cooperation with the gate array logic 42.

FIG. 2 shows a configuration of the intelligent battery 52 comprising anabnormal charging protection function in the embodiment. The intelligentbattery 52, to which the embodiment is applied, comprises in the batterypack a CPU 61 that is a microcomputer to perform processes for abnormalcharging protection, a voltage detection circuit 63 for detectingvoltage of battery cells 62 and notifying the CPU 61, and a currentdetection circuit 64 for measuring current flowing in the battery cells62 and notifying the CPU 61. It also comprises a discharging-stop FET 65(FET3) for protecting the intelligent battery 52 in abnormaldischarging, and a charging-stop battery FET 66 (FET4) for protectingthe intelligent battery 52 in abnormal charging.

The CPU 61 inputs a signal from the voltage detection circuit 63, andA/D converts it inside to monitor the battery voltage. For example, inthe case of lithium ion battery it is configured such that when voltageof the battery cells 62 reached 4.35 V or more per each one cell, itdetermines that abnormal charging is being performed and aborts chargingby turning off the charging-stop FET 66 (FET4). Specifically, sincevoltage of the battery in full charged state (100%) is 4.2 V (±50 mV)per cell, the CPU 61 is adapted to detect abnormal charging at 4.35V/cell in the light of detection error. The CPU 61, by communicationutilizing a communication line (COM1), transmits information aboutdetected abnormal charging to the embedded controller 41 (system-side),and also transmits to/receives from the embedded controller 41(system-side), various types of information such as information aboutbattery capacity or life.

FIGS. 3(a) and (b) show charging characteristics of a lithium ionbattery. FIG. 3(a) shows a characteristic for normal charging, and FIG.3(b) shows a characteristic for abnormal charging due to a failure. InFIGS. 3(a) and (b), the horizontal axis represents charging time(hours), and the vertical axis represents charging current (mA) andbattery capacity (%) to show battery capacity and charging current. Asshown in FIG. 3(a), in the normal charging, as the battery capacityincrease to a certain value (60% in FIG. 3(a)) or more, the chargerchanges its state from constant current charging to constant voltagecharging, then the charging current decreases. For example, in a typicalcharging manner, when the charging current value reach about 300 mA orless, it is determined that full charging is achieved, then thecharging-stops.

However, when main system is in power-off state, if a short-circuitfailure occurs in the FET3 or FET4, an abnormal charging like the oneshown in FIG. 3(b) takes place. In the example shown in FIG. 3(b), theAC adapter 51 has a characteristic of, for example, a constant voltageof 16 V and a constant current of 3.3 A (3300 mA). When a short circuitoccurs, the charging of the battery take place at 3.3 A until thecharging is aborted, specifically, until the charging is aborted bythe-protection circuit (charging stop FET 66), which, when the voltageper cell reaches 4.35 V or more, determines that abnormal charging takesplace, then operates. When the main system is in operation, since thepower is also fed to the main system, the charging current is low, forexample 2.0 A, but the charging of the battery also continues until theprotection circuit (charging stop FET66) operates.

Therefore, in this embodiment, the determination of malfunctionoccurrence in the battery is made by taking relationship between thebattery capacity and the charging current.

FIG. 4 shows a relationship between battery capacity and chargingcurrent during normal charging. In FIG. 4, the horizontal axisrepresents battery capacity (%), and the vertical axis representscharging current (mA). As shown in FIG. 4, as battery capacityincreases, typically, charging current decreases. Accordingly, when toolarge current flows for a battery capacity, it is possible to determinethat a malfunction occurs. Specifically, it is possible to predeterminea current value by which a malfunction is detected, and to detectmalfunction occurrence as soon as the detected charging currentincreases too much for the current value.

FIGS. 5(a) and (b) show an example of determination criteria formalfunction detection, which is used in this embodiment. FIG. 5(a) showsan example of a table for malfunction detection. FIG. 5(b) shows arelationship between abnormal current detection threshold value and theabnormal current according to the example of the FIG. 5(a). By referringto the table shown in FIG. 5(a), when a battery capacity (%) largecurrent more than the value shown in the table is detected, it ispossible to determine that a malfunction occurs. For example, as shownin FIG. 5(b), it is possible, as soon as current of 3.3 A flows, todetect that it is an abnormal current. It is also possible, when currentof 2.0 A flows, to determine that there is a malfunction at a time ofbattery capacity of 81%. In any of these cases, since the batterycapacity is less than 100%, and the protection circuit operates when thebattery voltage is 4.20 V/cell or less, any safety problem does notoccur. Regarding the values shown in FIG. 5(a), values of the batterycapacity are represented as integers. Values between the integers may beapproximated, for example, by rounding off.

Next, processes executed in this embodiment for achieving detection ofabnormal state and protection functions will be described.

FIG. 6 shows a block diagram of a process executed in the CPU 61 of theintelligent battery 52. In this embodiment, it comprises a chargingcurrent measurement unit 71 for measuring charging current in responseto output from the current detection circuit 64, and a battery capacityintegration unit 72 for calculating battery capacity based on chargingcurrent measured by the charging current measurement unit 71, or basedon the charging current and voltage from the voltage detection circuit63. The battery capacity integration unit 72 can calculate batterycapacity as electric charge amount (Ah) by integrating current valuewith respect to time, or battery capacity as electric energy (Wh) byintegrating current value multiplied by voltage value, with respect totime.

In an abnormal current detection table 73, a table, for example as shownin FIG. 5(a) is stored. An abnormal current determination unit 74compares value stored in the abnormal current detection table 73 andoutput results from the charging current measurement unit 71 and thebattery capacity integration unit 72, then determines if there is amalfunction. A charging protection FET off instruction unit 75, when theabnormal current determination unit determines that there is amalfunction, cause the charging-stop FET 66 (FET4) to operate to abortthe charging. A malfunction occurrence notification unit 76 is used inresponse to output of a malfunction occurrence from the abnormal currentdetermination unit 74 for notifying the embedded controller 41(system-side) of the occurrence of abnormal state.

FIG. 7 is a flow chart showing process flow in the case of using thetable shown in FIG. 5(a). The CPU 61 of the intelligent battery 52 atfirst determines if charging is being performed or not (step 101). Ifcharging is not being performed, then the process stands by, and ifcharging is being performed, then the charging current measurement unit71 measures charging current value (step 102). Then, the batterycapacity integration unit 72 derives integrated capacity (step 103). Theabnormal current determination unit 74 determines if the integratedcapacity is in the range of 0% to 70% (represented as approximationincluding decimals, same for later description), where 100% correspondsto the full capacity (step 104). If the condition is fulfilled, it isdetermined if the current value is 3.0 A or less, or not; if it is 3.0 Aor less, then the process returns to step 101 with recognition ofnormality; if it is more than 3.0 A, then the process goes tomalfunction processing with recognition of malfunction.

In the malfunction processing, in accordance with the chargingprotection FET off instruction unit 75, charging-stop process isperformed by the charging-stop FET 66 (FET4) that is a protectioncircuit (step 106). Then, the malfunction occurrence notification unit76 notifies the embedded controller 41 (system-side) of the malfunctionoccurrence (step 107). Then, in the system-side, the user is notified ofthe malfunction occurrence by using the LCD 18 (step 108), and themalfunction processing is completed.

If the condition of step 104 is not fulfilled at the abnormal currentdetermination unit 74, it is determined if the capacity is in the rangeof 71% to 80%, or not based on table information stored in the abnormalcurrent detection table 73 (step 109). If the capacity is in the range,it is determined if the current value is more than 2.5 A (step 110), ornot. If the current value is within 2.5 A, then the process returns tostep 101 with recognition of normality. If the current value is morethan 2.5 A, then the process goes to malfunction processing of steps 106to 108 with recognition of malfunction occurrence.

Similarly, it is determined, based on the table information stored inthe abnormal current detection table 73, if the capacity is in the rangeof 81% to 90%, or not (step 111). If the capacity is in the range of 81%to 90%, then it is determined if the current is within 2.0 A (step 112),or not. If the current value exceeds 2.0 A, then malfunction processingof steps 106 to 108 is performed. Similarly, it is determined if thecapacity is in the range of 91% to 95%, or not (step 113). If thecapacity is in the range of 91% to 95%, then it is determined if thecurrent value is within 1.3 A, or not (step 114). If the value exceeds1.3 A, then the malfunction processing of steps 106 to 108 is performed.Further, similarly, it is determined if the capacity is in the range of96% to 100%, or not (step 115). If the capacity is in the range of 96%to 100%, then it is determined if the current value is within 0.8 A(step 116), or not. If the current value exceeds 0.8 A, then themalfunction processing of steps 106 to 108 is performed. In the waydescribed above, by sequentially referring to values in a table formalfunction detection, for example as shown in FIG. 5(a), detection ofan abnormal state in the intelligent battery 52 is ensured.

Next, a detection method for detecting abnormal current by usingnumerical formulas instead of table information as shown in FIG. 5(a),which is stored in the abnormal current detection table 73, will bedescribed. For example, it is possible to derive approximation formulasfrom the relationship between battery capacity and charging current asshown in FIG. 4, and to detect an abnormal state based on theapproximation formulas. For example, from the relationship shown in FIG.4, numerical formulas for detection of abnormal current are derived asfollows:

Y=3100 (mA), for battery capacity X≦70%; and

Y=(60X+6700 (mA), for 71%<battery capacity X≦100%,

where Y represents abnormal current value, and X represents batterycapacity.

FIG. 8 is a flow chart showing a process flow for detection of abnormalstate based on numerical formulas described above. In the CPU 61 of theintelligent battery 52, at first it is determined if charging is beingperformed or not (step 201). If charging is not being performed, thenthe process stands by. If charging is being performed, charging currentis measured by the charging current measurement unit 71 (step 202), andintegrated capacity is obtained by the battery capacity integration unit72 (step 203). Then, an abnormal current value is calculated from theintegrated capacity by using the numerical formulas described above(step 204). Then, the abnormal current value obtained at step 204 iscompared with the charging current value measured at step 202 (step205). If the charging current value does not exceeds the abnormalcurrent value, then the process returns to step 201 with recognition ofnormal state.

If the charging current value exceeds the abnormal current value at step205, charging is stopped by charging-stop FET 66 (FET4) that is aprotection circuit (step 206). Then, the embedded controller 41 insystem-side is notified of malfunction occurrence (step 207). Then, inthe system-side, the malfunction occurrence is notified to the userthrough the LCD 18 (step 208), and the series of processes is completed.

As described above, in this embodiment, a mechanism for detectingabnormal charging in early stage and aborting the charging, is providedin the battery (intelligent battery 52). Even if the battery cell 62itself has a short-circuit problem, safety for the intelligent battery52 can be ensured unless charging with voltage that exceeds a predefinedvoltage because of abnormal charging is not performed. This embodimentcan provide a system, which is also safer even if a short-circuitproblem in the battery cell 62 itself and a problem of the chargingcircuit in the system-side occur. Additionally, when a malfunction isdetected by the abnormal charging detection mechanism in the batterypack (intelligent battery 52), the charging can be aborted, and theproblem occurrence can be notified to the user by notifying thesystem-side of the problem occurrence.

The relational characteristic as between battery capacity and chargingcurrent in normal charging, shown in FIG. 4, varies to some extentdepending on the type of battery (manufacturer). However, thesystem-side does not need to know difference between the battery typesor the like, since the abnormal current detection table 73 in thebattery includes table information shown in FIG. 5(a), for malfunctiondetection, and the CPU 61 in the battery determines malfunctionoccurrence and activates the protection circuit. The CPU 61 in thebattery pack, upon detection of a malfunction, activates the protectioncircuit (charging-stop FET 66 (FET4)) and notifies the system-side ofthe malfunction occurrence. The embedded controller 41, upon receivingnotification of malfunction occurrence from the battery (intelligentbattery 52), alerts the CPU 11 (the main processor). The CPU 11 that hasreceived the alert can notify the user of the malfunction occurrence bydisplaying the malfunction occurrence on the LCD 18, CRT monitor or thelike. In order to notify the user of malfunction occurrence, flashingLED or beep sound, for example, may be used.

Finally, an exemplary case will be described wherein the charger in themain system that is a notebook PC employsconstant-current/constant-voltage charging method, and the externalcharger employs pulse-charging method. The abnormal charging detectionmechanism in this embodiment can not used for a special-type chargerthat performs pulse-charging, for example, for lithium ion battery orlithium polymer battery. Pulse-charging is intended to perform rapidcharging, in which large current flows in pulse form with a chargingvoltage higher than a typical charging voltage. In such a case, when theconfiguration described above is used without any modification, chargingis aborted because it is determined that the charging current of theexternal charger is due to abnormal charging. In order to avoid this, aconfiguration is available, for example, wherein the device connected tothe battery (intelligent battery 52) uses a communication line (COM1)for sending identification information for the device, or ID to the CPU61 inside the battery. When CPU 61 recognizes connection of the batteryto the main system by ID, the abnormal charging detection mechanism inthis embodiment is enabled, and otherwise disabled. Such a configurationallows effective application of this embodiment in a possible case wherethe battery is connected to a charger with different charging modes.

As described above, the present invention provides a battery, which issafer even if dual accidental malfunctions occur.

What is claimed is:
 1. A power supply system with a battery forsupplying power to a main system, comprising: a charging currentmeasuring unit for measuring charging current for said battery; abattery capacity calculating unit for calculating battery capacity ofsaid battery; and a detecting unit for detecting malfunction occurringin said battery based on a charging current value obtained by saidcharging current measuring unit and said battery capacity calculated bysaid battery capacity calculating unit.
 2. The power supply systemaccording to claim 1, further comprising a protection facilityactivating unit for activating a protection facility based on detectionof malfunction occurrence by said detecting unit.
 3. The power supplysystem according to claim 1, further comprising a notification unit fornotifying said main system of malfunction based on detection of themalfunction occurrence by said detecting unit.
 4. A computer device,comprising: a main system for data processing; and an intelligentbattery for supplying power to said main system, wherein saidintelligent battery comprises: a battery cell for charging anddischarging, a current detection circuit for detecting charging currentfor said battery cell; and a CPU for calculating battery capacity byintegrating charging current detected by said current detection circuit,and recognizing malfunction occurring in the battery based on chargingcurrent value detected by the current detection circuit and thecalculated battery capacity.
 5. The computer device according to claim4, wherein said intelligent battery further comprises a protectioncircuit for performing stop operation according to instruction from theCPU based on recognition of malfunction occurrence by said CPU.
 6. Abattery for supplying power to an electric apparatus, comprising: acharging current measuring unit for measuring charging current for abattery cell; a battery capacity integration unit for integratingbattery capacity for said battery cell; and a malfunction detecting unitfor detecting malfunction occurrence based on a charging current valuemeasured by said charging current measuring unit and battery capacityintegrated by said battery capacity integration unit.
 7. The batteryaccording to claim 6, wherein said malfunction detecting unit detectsmalfunction occurrence based on information in a table for malfunctiondetection showing the relation between battery capacity and malfunctiondetection current value.
 8. The battery according to claim 6, whereinsaid malfunction detecting unit detects malfunction occurrence based onan equation representing the relation between battery capacity andcharging current value, which equation is separately defined accordingto battery capacity.
 9. A battery, comprising: a battery cell; a voltagedetection circuit for detecting voltage for said battery cell; a currentdetection circuit for detecting charging current for said battery cell;a charging stop unit for stopping charging for said battery cell; and acontrol unit for activating said charging stop unit based on voltagedetected by said voltage detection circuit, wherein before the voltagereaches a voltage for activating said charging stop unit, said controlunit detects a malfunction state based on a charging current valuedetected by said current detection circuit, and activates the chargingstop unit.
 10. The battery according to claim 9, wherein said controlunit calculates capacity of said battery cell, and if the chargingcurrent value detected for the calculated capacity by said currentdetection circuit is larger than a normal value, determines that amalfunction has occurred.
 11. The battery cell according to claim 9,wherein said control unit, when connected to an apparatus with a chargeremploying constant-current/constant-voltage charging mode, activatessaid the charging stop unit in response to said detection ofmalfunction.
 12. A method for protecting a battery from abnormalcharging, comprising: measuring a charging current value for saidbattery; calculating integrated capacity for said battery; andactivating a protection facility when the charging current valuemeasured for the calculated integrated capacity is larger than apredetermined value.
 13. The method according to claim 12, wherein theprotection facility is activated based on information specifying areference value representing a charging current value at which amalfunction is detected for an integration capacity.
 14. The methodaccording to claim 12, wherein the protection facility is activated in astate where said integrated capacity is less than 100%.
 15. A method forprotecting an intelligent battery with a microcomputer from abnormalcharging, comprising: recognizing that said intelligent battery isconnected to an apparatus with a charger forconstant-current/constant-voltage charging; measuring charging currentvalue when said intelligent battery is charged while switching fromconstant-current charging to constant-voltage charging; determiningbased on the measured charging current value whether abnormal chargingoccurs or not; and aborting charging when it is determined that abnormalcharging occurs.
 16. The method according to claim 15, wherein theconnection to said apparatus is recognized by receiving the ID of saiddevice.
 17. The method according to claim 15, wherein when it isdetermined that abnormal charging occurs, said apparatus is notified ofthe occurrence of abnormal charging.
 18. A program of software-basedcode for enabling a microcomputer contained in a battery to perform: acharging function for measuring charging current value for said battery;a calculating function for calculating integrated capacity in saidbattery; and a protecting function for activating a protection facilitywhen the charging current value measured for the calculated integratedcapacity is larger than a predetermined value.
 19. A program forenabling a microcomputer contained in a battery to perform: a functionfor recognizing that said battery is connected to an apparatus with acharger for constant-current/constant-voltage charging; a function formeasuring charging current value when said battery is charged whileswitching from constant-current charging to constant-voltage charging; afunction for determining based on the measured charging current valuewhether abnormal charging occurs or not; and a function for abortingcharging when it is determined that abnormal charging occurs.